Hi rAthena!
Can anyone kindly share a link on a "Latest Stable Client + Clean Server Files with working Title and Achievement System" 2015 and above maybe, if there is one?
I'm willing to pay also if necessary just send me a PM and we'll talk about the price.
Sorry, I can't seem to make my own because I'm using a very old PC. All it can manage is adding Custom Items, Monsters, Maps, etc. But building a server from scratch, some needed programs can't be installed.
Hope someone will hear me out.

Origin:
So my inspiration for this script is taken from "Aura Kingdom".
If you've played that, you'll know. lol
And.. This is a small piece of my Servers Storyline so, my full gratitude goes to Sir Sehrentos for this!
Mechanics:
Triggers automatically.
It will announce the name of the Monster to be spawned and what map it should spawn.
You need a party to be able to kill it.
Once killed, a Treasure Box will spawn but only the Party Leader can open the Treasure Box and Distribute the Rewards on Randomly to every Party Members.
The Treasure Box reward has 4 tiers to choose from and it chooses Random List of Rewards everytime it is opened.
Once all the reward has been distributed, you'll need to wait again for the next World Boss Spawn.
You Can:
Set on what time the World Boss you want to spawn automatically.
Set any mobs you want to be the World Boss just replace the Mob IDs with your Custom ones.
Set on what map you want the World Boss to spawn. (orignally set to random map)
Set the Item Rewards from the Treasure Box.
Credits:
Basically, this was my idea, but Sir Sehrentos has given all his efforts on helping me with this script, so He deserves all the credit.
Main Script:
[World Boss]
https://pastebin.com/x1SGnE3e
Anti Abuse:
Cause CHAMPS has the tendency to lure the World Boss near the healer and just Heal + Asura then they can solo the World Boss which is againt's the original purpose.
Healer NPC is deactivated when World Boss is active in a particular map.
https://pastebin.com/CfL3tCb4
Healer NPC Credit goes to Master Euphy!
NOTE:
If you have any suggestions for improvement, kindly comment it down.